1. Field of the Invention
The present invention relates to rechargeable electronic devices, and more particularly to a method and apparatus for recharging batteries used to power a rechargeable electronic device, such as a wrist watch computer.
2. Description of the Related Art
Rechargeable electronic devices use rechargeable batteries, such as NiCd (nickel cadmium), NiMH (nickel-metal hydride) and lithiuim-based batteries. Conventionally, the rechargeable batteries are recharged by supplying current through wires that are connected to the electronic device. The electronic device may have external electrical contacts for receiving electrical energy from an external power supply to recharge the batteries. Such external electrical contacts may be prone to poor performance, or even failure, due to becoming dirty or corroded. Further, electrical contacts are undesirable for use with electronic devices that are exposed to water, because the electrical contacts make the electronic device difficult to water proof.
Alternatively, contact-less charging using induction has been used in electronic devices, such as motorized toothbrushes and cordless phones. According to this conventional method, an inductively rechargeable electronic device is placed in an inductive charger. The inductive charger includes a primary coil and the electronic device includes a secondary coil. Alternating current flows through the primary coil of the inductive charger, causing a varying magnetic field that is used by the secondary coil in the electronic device to generate energy. The energy generated by the secondary coil is then used to charge the battery in the electronic device.
Although inductive charging obviates the need for contacts, such a method is not practical for use with smaller electronic devices because such devices do not have enough space to fit a coil large enough to generate energy to charge a battery. Further, the coil may interfere with the ability of the electronic device to communicate using radio frequency.